KR101767899B1 - Method for manufacturing zinc-doped alumina dehydrogenation catalyst - Google Patents

Abstract

The present invention relates to a process for the production of gamma-alumina, comprising the steps of: transforming spherical gamma-alumina to heat-treated gamma-alumina or cetal-alumina through heat treatment; Treating the heat-treated gamma-alumina and theta-alumina in a solution of zinc nitrate (Zn (NO ₃ ) ₂ 6H ₂ O) as a precursor of zinc oxide (ZnO); And calcining the mixture at a temperature of 700 to 1,200 ° C. The present invention also provides a method for producing a zinc-doped alumina dehydrogenation catalyst.
The zinc-doped alumina dehydrogenation catalyst according to the present invention has an effect of improving selectivity, stability, and service life by doping zinc with alumina having controlled pore characteristics.

Description

METHOD FOR MANUFACTURING ZINC-DOPED ALUMINA DEHYDROGENATION CATALYST BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a process for preparing a zinc-doped alumina dehydrogenation catalyst, and more particularly, to a process for preparing a zinc-doped alumina dehydrogenation catalyst having improved purity, stability, and lifetime by doping zinc with alumina having controlled pore characteristics.

Dehydrogenation catalysts are divided into two categories: chromium catalysts and platinum catalysts. The chromium-based catalyst has a problem in that the lifetime of the catalyst is shorter than that of the platinum-based catalyst and the toxicity of the chromium itself due to the rapid deactivation of the catalyst due to the generation of coke and the rapid regeneration rate thereof. However, platinum-based catalysts are widely used because of their excellent dehydrogenation catalyst activity and stability and long catalyst lifetime. As the carrier of the catalyst, alumina, silica and zeolite are widely used. The properties required for such a dehydrogenation catalyst should include the content of the active ingredient, the type of promoter, the dispersity of the active ingredient, the type of carrier, the pore characteristics of the carrier, and the acidity of the carrier. Particularly, The initial activity of the catalyst plays a very important role, and when the catalyst is used for a long time in the process, sintering of the active metal component proceeds to lower the dispersibility and eventually decrease the activity (Catalysis Today 111 (2006) 133-139). Therefore, there is a need for a process for preparing a catalyst having a high active ingredient dispersion.

The platinum catalyst is generally prepared by the following room temperature / high temperature adsorption support method. Dissolve chloroplatinic acid, hydrochloric acid, and nitric acid in distilled water and add a certain amount of carrier. After sufficiently stirring at room temperature, drying and heat treatment are performed. Thereafter, the components used as the promoter are dissolved in distilled water and adsorbed and supported in the same manner as in the case of platinum.

To the chloroplatinic acid (H2PtCl6) solution, neutralize with sodium hydrogen sulfite (NaHSO3), dilute with water, add sodium hydroxide to the diluent, and adjust to pH 5. Subsequently, the carrier is added, sodium hydroxide is added to adjust the pH to 5, and then a reducing agent is added to reduce the platinum. Finally, when the reaction product is filtered, washed, and dried, a platinum catalyst powder in which fine platinum particles are precipitated on the support powder is obtained. However, when the platinum-based catalyst is prepared by the above-described method, the size and the dispersed form of the platinum particles are not uniform, and since the reduction of the platinic acid occurs temporarily and the platinum particles precipitate rapidly on the surface of the support, There is a problem that it is difficult. Further, there is a difficulty in controlling pH at each step.

 U.S. Patent No. 5,068,161 discloses a process for producing a platinum-supported catalyst by dissolving chloroplatinic acid in an excess amount of water as a solvent, reducing it with formaldehyde as a reducing agent, filtering the solvent to remove the solvent, Reduction method, but the size of the catalyst particles rapidly changes according to the reducing agent, and when the concentration is 30 wt% or more, the size of the catalyst particles becomes too large.

H. Wendt (H. Wendt et al., Electrochim. Acta, 43, 1998), after dissolving a catalyst raw material by using an excessive amount of solvent, impregnating the carbon support with a carbon carrier, , A method of preparing a carbon supported catalyst by reducing with hydrogen gas has been proposed. However, since the concentration gradient occurs in the drying step, the metal salt due to the capillary phenomenon may flow out to the surface of the carrier. As the content of platinum increases, Is increased.

It is an object of the present invention to provide a method of preparing a zinc-doped alumina dehydrogenation catalyst having improved purity, selectivity, stability, and life span by doping alumina with zinc.

In accordance with one aspect of the present invention, there is provided a method of forming a gamma-alumina, comprising: transforming spherical gamma-alumina to heat-treated gamma-alumina or cetal-alumina; Treating the heat-treated gamma-alumina and theta-alumina in a solution of zinc nitrate (Zn (NO ₃ ) ₂ 6H ₂ O) as a precursor of zinc oxide (ZnO); And calcining the mixture at a temperature of 700 to 1,200 ° C. The present invention also provides a method for producing a zinc-doped alumina dehydrogenation catalyst. At this time, if the calcination temperature is lower than 700 ° C or higher than 1200 ° C, the selectivity, stability and lifetime of the catalyst may be lowered

Also, the amount of zinc oxide produced from the zinc nitrate is 0.001 to 0.1 mole ratio relative to the total amount of the alumina (which means the total molar amount of the heat-treated gamma-alumina or theta-alumina), and the heat treated gamma- Wherein the alumina has bimodal pore characteristics. The present invention also provides a method for preparing a zinc-doped alumina dehydrogenation catalyst. If the amount of the zinc oxide is less than 0.001 mol or less than 0.1 mol based on the total amount of the alumina, the selectivity, stability and lifetime of the dehydrogenation catalyst may be deteriorated.

In addition, the zinc-doped alumina dehydrogenation catalyst has a selectivity of 94.0 to 95.0 wt% and an average coke production of 0.6 to 1.3 wt% / hr. do.

The zinc-doped alumina dehydrogenation catalyst according to the present invention has an effect of improving selectivity, stability, and service life by doping zinc with alumina having controlled pore characteristics.

The zinc-doped alumina dehydrogenation catalyst according to the present invention can be obtained by phase-transforming spherical alumina (gamma-alumina) with heat-treated gamma-alumina or cetal-alumina having bimodal pore characteristics (Meso and Macro) Followed by carrying zinc on the prepared gamma-alumina or theta-alumina support by adsorption-assisted method. At this time, the amount of zinc oxide produced from the zinc nitrate in the loading process is 0.001 to 0.1 mole ratio relative to the total amount of the alumina (which means the total molar amount of the heat-treated gamma-alumina or theta-alumina)

The alumina carrier is preferably a gamma-phase or a ceta-phase of alumina and has a formability of 90% or more. In the case of gamma-alumina, there is a large negative reaction due to the acid sites of alumina itself, a change in structural characteristics such as alumina crystallinity and reduced specific surface area during the reaction, It is possible to prevent a negative effect. In the case of alpha-alumina, the low specific surface area lowers the dispersibility of the metal and reduces the overall active area of the metal, thereby exhibiting low catalytic activity. The alumina support may use a gamma phase or a ceta phase depending on the heat treatment temperature and time.

The alumina support has a specific surface area of 70 to 170 m 2 / g, a mesopore of 5 to 100 nm and a macropore of 100 to 20,000 nm. If the specific surface area of the support is less than 70 m < 2 > / g, the dispersibility of the metal active component is lowered. When the specific surface area exceeds 170 m2 / g, the gamma crystallinity of alumina is maintained to be high.

The volume and pore size of the carrier pore are the main factors that determine the mass transfer coefficient of reactants and products. In the case of rapid chemical reaction rate, the diffusion resistance of the material determines the overall reaction rate, Which is advantageous in maintaining high activity of the enzyme. Further, the use of a carrier having a large pore size is insensitive to the scale of the coke, which is advantageous for maintaining the catalytic activity.

The catalyst has a high degree of dispersion when the active ingredient is supported, and the development of meso and macropores has the effect of increasing the mass transfer rate. That is, when the size of the pores existing in the catalyst is large, it is insensitive to reduction of the activity due to the coke generated on the catalyst, and exhibits high reaction activity even when the liquid space velocity increases due to the high mass transfer rate.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the following examples are intended to illustrate preferred embodiments of the present invention, and the scope of the present invention is not limited by the following examples.

Example  One

A spherical commercial alumina having a gamma crystallinity and an average diameter of 1.65 mm and a packing density of 0.56 g / ml was purchased from the carrier used for the catalyst synthesis, and was thermally deformed at a temperature of 1050 ° C for 6 hours in an air atmosphere Phase. Crystallinity of theta alumina was measured by Xray analysis and found to be 90% or higher.

The catalyst was prepared by using the heat-treated heat-treated theta-alumina support at room temperature / temperature adsorption support. Zn nitrate (Zn (NO ₃ ) ₂ 6H ₂ O), which is a precursor of zinc oxide (ZnO), was dissolved in distilled water and then heat-deformed theta-alumina was added thereto. The supported liquid was dried using a rotary evaporator, stirred at room temperature for 1.5 hours at 25 rpm, and then dried at 80 ° C. for 1.5 hours at 25 rpm under reduced pressure. For complete drying, it was dried in an oven at 105 ° C for 15 hours and then calcined in a heating furnace at 700 ° C for 2 hours. At this time, the amount of zinc oxide produced from the zinc nitrate is 0.001 mole ratio relative to the total amount of the alumina (which means the total molar amount of the heat-deformed theta-alumina).

Example  2

The amount of zinc oxide produced from zinc nitrate using gamma-alumina thermally deformed with the carrier was 0.1 molar ratio with respect to the total amount of alumina (which means the total molar amount of the heat-deformed gamma-alumina) The same catalyst was prepared.

Comparative Example  One

Tin chloride (SnCl2), hydrochloric acid (HCl), and nitric acid (HNO3) were dissolved in distilled water and then heat-deformed alumina was added to the solution. The supported liquid was dried using a rotary evaporator, stirred at room temperature for 1.5 hours at 25 rpm, and then dried at 80 ° C. for 1.5 hours at 25 rpm under reduced pressure. For complete drying, it was dried in an oven at 105 ° C for 15 hours and heat-treated at 700 ° C for 2 hours. Thereafter, the alumina bearing the tin was loaded in distilled water containing chloroplatinic acid (H2PtCl66H2O), hydrochloric acid (HCl), and nitric acid (HNO3). The supported liquid was dried using a rotary evaporator, stirred at room temperature for 1.5 hours at 25 rpm, and then dried at 80 ° C. for 1.5 hours at 25 rpm under reduced pressure. For complete drying, it was dried in an oven at 105 ° C for 15 hours and heat-treated at 700 ° C for 2 hours.

Experimental Example

- Performance test of dehydrogenation catalyst -

In order to confirm the performance of the dehydrogenation catalyst according to the present invention, the following experiment was conducted.

2.4 ml of the catalyst prepared in Examples 1 and 2 and Comparative Example 1 were packed in a quartz reactor having a volume of 7 ml, respectively, and a dehydrogenation reaction was carried out by supplying a mixed gas of propane and hydrogen. At this time, the ratio of hydrogen to propane was fixed at 1: 1, and the dehydrogenation reaction was carried out under adiabatic conditions while maintaining the reaction temperature at 620 ° C., the absolute pressure at 1.5 atm, and the liquid space velocity at 15 hr -1. The gas composition after the reaction was analyzed by gas chromatography coupled with the reactor to determine propane conversion and propylene selectivity in the product after reaction.

The rates, selectivity and yields at 5 hours after the start of the reaction are shown in the table.

division Conversion Rate Selectivity Average coke production Example 1 36.5 wt% 94.7 wt% 1.3 wt% / hr Example 2 35.5 wt% 95.0 wt% 0.6 wt% / hr Comparative Example 1 37.9 wt% 93.9 wt% 3.5 wt% / hr

As shown in Table 1, Examples 1 and 2 of the present invention are superior in reaction selectivity to the Comparative Examples. The propane conversion was maintained at a similar level when compared with the comparative example. In addition, the 5-hour average coke production amount was found to be decreased in the embodiment as compared with the comparative example.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Will be apparent to those skilled in the art. Accordingly, the scope of protection of the present invention should be defined in the appended claims and their equivalents.

Claims (3)

Transforming spherical gamma-alumina into heat-treated theta-alumina through heat treatment;
Treating the heat-treated theta-alumina in a solution containing zinc nitrate (Zn (NO ₃ ) ₂ 6H ₂ O) as a precursor of zinc oxide (ZnO); And
And firing at a temperature of 700 to 1200 DEG C,
The amount of zinc oxide produced from the zinc nitrate is 0.001 to 0.1 mole ratio relative to the total molar amount of the heat-treated theta-alumina,
The heat-treated theta-alumina has bimodal pore characteristics,
Wherein the selectivity is 94.0 to 95.0 wt%, and the average amount of coke produced is 0.6 to 1.3 wt% / hr. delete delete